Plants belonging to the genus Glychyrrhiza are perennial herbaceous plants belonging to the family Fabaceae. Among raw materials for Chinese herbal medicines, underground roots and stolons of plants belonging to the genus Glychyrrhiza are important ones, and they are widely used for pharmaceuticals worldwide. A main active ingredient of the plants belonging to the genus Glychyrrhiza, Glychyrrhiza uralensis, Glychyrrhiza glabra, and Glychyrrhiza inflata is glycyrrhizin, which is a triterpene saponin. Numerous studies have been conducted on glycyrrhizin from various perspectives such as pharmacognostic study, pharmacological study, and breeding study. Yet, regarding the biosynthetic pathway of glycyrrhizin, it has been absolutely unknown how glycyrrhizin is biosynthesized following β-amyrin, which is a triterpene. In order to stably and continuously supply a good quality herbal medicine, establishment of optimal conditions for production, selection of a high-production strain, and the like are necessary using a biosynthesis gene itself of glycyrrhizin, which is an active ingredient, or a gene expression thereof as a marker. However, such an approach has not been able to be implemented because the biosynthetic pathway is unknown. Also, molecular breeding of a plant producing a large amount of glycyrrhizin by introduction of the biosynthesis gene has not been able to be realized.
The biosynthesis pathway of soyasapogenol B from β-amyrin has been well studied, and CYP93E (FIG. 1), a gene encoding an enzyme which hydroxylates β-amyrin at the position 24, is disclosed in International Publication WO/2005/080572 and by Shibuya et al. in Identification of beta-amyrin and sophoradiol 24-hydroxylase by expressed sequence tag mining and functional expression assay., FEBS J. 2006 March; 273(5): 948-59.